The present disclosure relates generally to stateless call admission and call preemption with a single metering and marking scheme.
The IETF (Internet Engineering Task Force) is investigating methods for controlling the admitted load of voice (and multimedia) traffic over a packet network without support of per flow, or even per aggregate, states in the core. (See, B. Briscoe et al., “A Framework for Admission Control over DiffServ using Pre-Congestion Notification”, IETF draft-briscoe-tsvwg-cl-architecture-03.txt, Jun. 26, 2006 and B. Briscoe et al., “Pre-Congestion Notification Marking”, IETF draft-briscoe-tsvwg-cl-phb-02.txt, Jun. 26, 2006, which are both incorporated by reference herein in their entirety). This can be referred to as a CAC (Call Admission Control) approach over a stateless core.
The method relies on core nodes providing explicit notification information to edge nodes when the traffic load on a core link reaches certain levels. The edge nodes use some of this explicit notification information to decide whether new calls should be accepted. This is referred to as a flow “Admission” process. The edge nodes may also use some explicit notification information to drop calls that are already in place if needed. This is referred to as a flow “Preemption” process.
In order to provide the explicit notification information, the core node meters voice traffic load on each link, and when it reaches predefined thresholds the core node sets particular bits in the header of packets (PCN-bits (pre-congestion notification-bits)).
An important requirement for this method is that the Admission and Preemption processes are able to react at different load thresholds. For example, a network operator policy may be to stop admitting new voice calls when the load through a given link reaches 50%, but only start dropping calls when the load exceeds 70%.
Because of this requirement, the solutions proposed in IETF typically involve separate metering/marking schemes for Admission and for Preemption. In core routers, the traffic is metered against the Admission Threshold, and if in excess, a codepoint is set in the PCN-bits indicating “Admission Threshold exceeded”. The traffic is also metered against the Preemption Threshold, and if in excess, another codepoint is set in the PCN-bits indicating “Preemption Threshold exceeded”.
One approach proposed in IETF does not require preemption marking, however, it does require two separate measurement schemes; one measurement for Admission and another measurement for Preemption/Dropping. Furthermore, this approach mandates that the configured preemption rate is set to a drop rate. This is a significant restriction in that it results in preemption only taking effect once packets actually get dropped.